# 读取输入的笔记本数量
n = int(input())

# 计算不打折的总价
total_price_without_discount = (3 + 5) * n

# 计算打折后的总价
total_price_with_discount = (3 + 5) * n * 0.8

# 计算节省的费用
savings = total_price_without_discount - total_price_with_discount

# 输出节省的费用，精确到小数点后2位
print(f"{savings:.2f}")